
/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
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 *版权所有2002-2017原作者。
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 *根据Apache许可证2.0版（“许可证”）获得许可；
 *除非符合许可证，否则不得使用此文件。
 *您可以在以下地址获取许可证副本：
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package org.springframework.beans.factory.config;

import java.io.Serializable;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * A {@link org.springframework.beans.factory.FactoryBean} implementation that
 * returns a value which is an {@link org.springframework.beans.factory.ObjectFactory}
 * that in turn returns a bean sourced from a {@link org.springframework.beans.factory.BeanFactory}.
 *
 * <p>As such, this may be used to avoid having a client object directly calling
 * {@link org.springframework.beans.factory.BeanFactory#getBean(String)} to get
 * a (typically prototype) bean from a
 * {@link org.springframework.beans.factory.BeanFactory}, which would be a
 * violation of the inversion of control principle. Instead, with the use
 * of this class, the client object can be fed an
 * {@link org.springframework.beans.factory.ObjectFactory} instance as a
 * property which directly returns only the one target bean (again, which is
 * typically a prototype bean).
 *
 * <p>A sample config in an XML-based
 * {@link org.springframework.beans.factory.BeanFactory} might look as follows:
 *
 * <pre class="code">&lt;beans&gt;
 *
 *   &lt;!-- Prototype bean since we have state --&gt;
 *   &lt;bean id="myService" class="a.b.c.MyService" scope="prototype"/&gt;
 *
 *   &lt;bean id="myServiceFactory"
 *       class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean"&gt;
 *     &lt;property name="targetBeanName"&gt;&lt;idref local="myService"/&gt;&lt;/property&gt;
 *   &lt;/bean&gt;
 *
 *   &lt;bean id="clientBean" class="a.b.c.MyClientBean"&gt;
 *     &lt;property name="myServiceFactory" ref="myServiceFactory"/&gt;
 *   &lt;/bean&gt;
 *
 *&lt;/beans&gt;</pre>
 *
 * <p>The attendant {@code MyClientBean} class implementation might look
 * something like this:
 *
 * <pre class="code">package a.b.c;
 *
 * import org.springframework.beans.factory.ObjectFactory;
 *
 * public class MyClientBean {
 *
 *   private ObjectFactory&lt;MyService&gt; myServiceFactory;
 *
 *   public void setMyServiceFactory(ObjectFactory&lt;MyService&gt; myServiceFactory) {
 *     this.myServiceFactory = myServiceFactory;
 *   }
 *
 *   public void someBusinessMethod() {
 *     // get a 'fresh', brand new MyService instance
 *     MyService service = this.myServiceFactory.getObject();
 *     // use the service object to effect the business logic...
 *   }
 * }</pre>
 *
 * <p>An alternate approach to this application of an object creational pattern
 * would be to use the {@link ServiceLocatorFactoryBean}
 * to source (prototype) beans. The {@link ServiceLocatorFactoryBean} approach
 * has the advantage of the fact that one doesn't have to depend on any
 * Spring-specific interface such as {@link org.springframework.beans.factory.ObjectFactory},
 * but has the disadvantage of requiring runtime class generation. Please do
 * consult the {@link ServiceLocatorFactoryBean ServiceLocatorFactoryBean JavaDoc}
 * for a fuller discussion of this issue.
 *
 * @author Colin Sampaleanu
 * @author Juergen Hoeller
 * @since 1.0.2
 * @see org.springframework.beans.factory.ObjectFactory
 * @see ServiceLocatorFactoryBean
 */
/**
 *一个{@link.org.springframework.beans.factory.FactoryBean}实现
 *返回一个｛@link org.springframework.beans.factory.ObjectFactory｝值
 *这反过来又返回一个源于{@linkorg.springframework.beans.factory.BeanFactory}的bean。
 *
 *＜p＞因此，这可以用来避免客户端对象直接调用
 *｛@link org.springframework.beans.factory.BeanFactory#getBean（String）｝获取
 *来自
 *｛@link org.springframework.beans.factory.BeanFactory｝，它将是一个
 *违反控制反转原则。相反，使用
 *在这个类中，客户端对象可以被
 *｛@link org.springframework.beans.factory.ObjectFactory｝实例作为
 *属性，该属性仅直接返回一个目标bean（同样
 *通常是原型bean）。
 *
 *＜p＞基于XML的示例配置
 *｛@link org.springframework.beans.factory.BeanFactory｝可能如下所示：
 *
 *<pre-class=“code”>&lt；豆类&gt；
 *
 *&lt；！--原型bean，因为我们有状态--&gt；
 *&lt；bean id=“myService”class=“a.b.c.myService”scope=“prototype”/&gt；
 *
 *&lt；bean id=“myServiceFactory”
 *class=“org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean”&gt；
 *&lt；property name=“targetBeanName”&gt&书信电报；idref local=“myService”/&gt&lt/属性&gt；
 *&lt/豆&gt；
 *
 *&lt；bean id=“clientBean”class=“a.b.c.MyClientBean”&gt；
 *&lt；property name=“myServiceFactory”ref=“myServiceFactory”/&gt；
 *&lt/豆&gt；
 *
 *&lt/豆类&gt</前>
 *
 *＜p＞助理｛@code MyClientBean｝类实现可能看起来
 *类似于：
 *
 *<pre-class=“code”>包a.b.c；
 *
 *导入org.springframework.beans.factory.ObjectFactory；
 *
 *公共类MyClientBean{
 *
 *私有ObjectFactory&lt；我的服务&gt；myServiceFactory；
 *
 *public void setMyServiceFactory（ObjectFactory&lt；MyService&gt；myServiceFactory）{
 *this.myServiceFactory=myServiceFactory；
 *   }
 *
 *public void someBusinessMethod（）{
 *//获取一个全新的MyService实例
 *MyService服务=this.myServiceFactory.getObject（）；
 *//使用服务对象来实现业务逻辑。。。
 *   }
 *}</pre>
 *
 *＜p＞另一种应用对象创造模式的方法
 *将使用｛@link ServiceLocatorFactoryBean｝
 *源（原型）bean。｛@link ServiceLocatorFactoryBean｝方法
 *有一个优点，那就是一个人不必依赖任何人
 *特定于Spring的接口，例如{@link.org.springframework.beans.factory.ObjectFactory}，
 *但是具有需要生成运行时类的缺点。请这样做
 *查阅｛@link ServiceLocatorFactoryBean ServiceLocatorFactoryBean JavaDoc｝
 *以便更充分地讨论这个问题。
 *
 *@作者Colin Sampaleanu
 *@作者Juergen Hoeller
 *@自1.0.2起
 *@参见org.springframework.beans.factory.ObjectFactory
 *@参见ServiceLocatorFactoryBean
 */
public class ObjectFactoryCreatingFactoryBean extends AbstractFactoryBean<ObjectFactory<Object>> {

	@Nullable
	private String targetBeanName;


	/**
	 * Set the name of the target bean.
	 * <p>The target does not <i>have</i> to be a non-singleton bean, but realistically
	 * always will be (because if the target bean were a singleton, then said singleton
	 * bean could simply be injected straight into the dependent object, thus obviating
	 * the need for the extra level of indirection afforded by this factory approach).
	 */
	/**
	 *设置目标bean的名称。
	 *＜p＞目标不是＜i＞必须是非单例bean，而是现实的
	 *始终是（因为如果目标bean是singleton，则表示singleton
	 *bean可以直接注入依赖对象，从而避免
	 *这种工厂方法提供的额外间接级别的需要）。
	 */
	public void setTargetBeanName(String targetBeanName) {
		this.targetBeanName = targetBeanName;
	}

	@Override
	public void afterPropertiesSet() throws Exception {
		Assert.hasText(this.targetBeanName, "Property 'targetBeanName' is required");
		super.afterPropertiesSet();
	}


	@Override
	public Class<?> getObjectType() {
		return ObjectFactory.class;
	}

	@Override
	protected ObjectFactory<Object> createInstance() {
		BeanFactory beanFactory = getBeanFactory();
		Assert.state(beanFactory != null, "No BeanFactory available");
		Assert.state(this.targetBeanName != null, "No target bean name specified");
		return new TargetBeanObjectFactory(beanFactory, this.targetBeanName);
	}


	/**
	 * Independent inner class - for serialization purposes.
	 */
	/**
	 *独立的内部类-用于序列化目的。
	 */
	@SuppressWarnings("serial")
	private static class TargetBeanObjectFactory implements ObjectFactory<Object>, Serializable {

		private final BeanFactory beanFactory;

		private final String targetBeanName;

		public TargetBeanObjectFactory(BeanFactory beanFactory, String targetBeanName) {
			this.beanFactory = beanFactory;
			this.targetBeanName = targetBeanName;
		}

		@Override
		public Object getObject() throws BeansException {
			return this.beanFactory.getBean(this.targetBeanName);
		}
	}

}
